The three divisions of the book

The Acts of the Apostles are divided essentially into three parts
-- Acts 1, Acts 2 to 12; and Acts 13 to the end. Acts 11 and Acts 12
may be termed transitional chapters founded on the event related in
Acts 10. Acts 1 gives us that which is connected with the Lord's
resurrection; Acts 2-12 that work of the Holy Ghost of which
Jerusalem and the Jews were the centre, but which branches out into
the free action of the Spirit of God, independent of, but not
separated from, the twelve and Jerusalem as the centre; Acts 13, and
the succeeding chapters, the work of Paul, flowing from a more
distinct mission from Antioch; Acts 15 connecting the two in order
to preserve unity in the whole course. We have indeed the admission
of Gentiles in the second part, but it is in connection with the
work going on among the Jews. These latter had rejected the witness
of the Holy Ghost to a glorified Christ, as they had rejected the
Son of God in His humiliation; and God prepared a work outside them,
in which the apostle of the Gentiles laid foundations that annulled
the distinction between Jew and Gentile, and which unite them -- as
in themselves equally dead in trespasses and sins -- to Christ, the
Head of His body, the assembly, in heaven.*

{*It is a sorrowful but instructive thing to see, in the last
division of the book, how the spiritual energy of a Paul closes, as
to its effect in work, in the shadow of a prison. Yet we see the
wisdom of God in it. The boasted apostolicism of Rome never had an
apostle but as a prisoner; and Christianity, as the Epistle to the
Romans testifies, was already planted there.}